Method Of Preheating Beer In An Ethanol Plant

ABSTRACT

A method for preheating beer including providing a first heat exchanger, comprising a first outlet stream at a first temperature; providing a second heat exchanger, comprising a hot heat transfer stream, a first flow control valve situated within said hot heat transfer stream, a second outlet stream at a second temperature, a temperature sensor situated within said second outlet stream; wherein said first outlet fluid comprises a first inlet stream, and a second flow control valve situated within said first inlet stream; determining said second temperature with said temperature sensor; comparing said second temperature to a predetermined temperature range; performing an operation selected from the group consisting of: maintaining said first flow control valve in a closed position, and maintaining said second flow control valve in an open position, if said second temperature is within said predetermined temperature range, modulating said first flow control valve in order to effect heat transfer between said hot heat transfer fluid and said first inlet fluid, such that said second temperature within said predetermined temperature range, and maintaining said second flow control valve in an open position, determining if said second temperature is not within said predetermined temperature range if said first control valve is in the fully open position, and then closing said second flow control valve, closing said first flow control valve, and redirecting said first outlet stream away from said second heat exchanger is provided.

This application claims the benefit of U.S. Provisional Application No. 61/077,990, filed Jul. 3, 2008, the entire contents of which are incorporated herein by reference.

BACKGROUND

A variety of cereal grains and other plants are grown for use as food. Major cereal grains include corn, rice, wheat, barley, sorghum (milo), millets, oats, and rye. Other plants include potatoes, cassava, and artichokes. Corn is the most important cereal grain grown in the United States. A mature corn plant consists of a stalk with an ear of corn encased within a husk. The ear of corn consists of about 800 kernels on a cylindrical cob. The kernels are eaten whole and are also processed into a wide variety of food and industrial products. The other parts of the corn plant (i.e., the stalk, leaves, husk, and cob) are commonly used for animal feed, but are sometimes processed into a variety of food and industrial products.

In more detail, the corn kernel consist of three main parts: (1) the pericarp; (2) the endosperm; and (3) the germ. The pericarp (also known as the seed coat or bran) is the outer covering of the kernel. It consists primarily of relatively coarse fiber. The endosperm is the energy reserve for the plant. It consists primarily of starch, protein (also known as gluten), and small amounts of relatively fine fiber. The germ (also known as the embryo) consists primarily of oil and a miniature plant with a root-like portion and several embryonic leaves.

Starch is stored in a corn kernel in the form of discrete crystalline bodies known as granules. Starch is a member of the general class of carbohydrates known as polysaccharides. Polysaccharides contain multiple saccharide units (in contrast to disaccharides which contain two saccharide units and monosaccharides which contain a single saccharide unit). The length of a saccharide chain (the number of saccharide units in it) is sometimes described by stating its “degree of polymerization” (abbreviated to D.P.). Starch has a D.P. of 1000 or more. Glucose (also known as dextrose) is a monosaccharide (its D.P. is 1). Saccharides having a D.P. of about 5 or less are sometimes referred to as sugars.

As mentioned above, the pericarp and endosperm of the corn kernel contain fiber. The fiber comprises cellulose, hemicellulose, lignin, pectin, and relatively small amounts of other materials. Fiber is present in relatively small amounts in the corn kernel, but is present in much greater amounts in other corn components such as the cob, husk, leaves, and stalk. Fiber is also present in other plants. The combination of cellulose and lignin is sometimes known as lignocellulose and the combination of cellulose, lignin, and hemicellulose is sometimes known as lignocellulosic biomass. As used herein, the term “fiber” (and its alternative spelling “fibre”) refers to cellulose, hemicellulose, lignin, and pectin.

A wide variety of processes have been used to separate the various components of corn. These separation processes are commonly known as corn refining. One of the processes is known as the dry milling process. In this process, the corn kernels are first cleaned and then soaked in water to increase their moisture content. The softened corn kernels are then ground in coarse mills to break the kernel into three basic types of pieces--pericarp, germ, and endosperm. The pieces are then screened to separate the relatively small pericarp and germ from the relatively large endosperm. The pericarp and the germ are then separated from each other. The germs are then dried and the oil is removed. The remaining germ is typically used for animal feed. The endosperm (containing most of the starch and protein from the kernel) is further processed in various ways. As described below, one of the ways is to convert the starch to glucose and then ferment the glucose to ethanol.

Fermentation is a process by which microorganisms such as yeast digest sugars to produce ethanol and carbon dioxide. Yeast reproduce aerobically (oxygen is required) but can conduct fermentation anaerobically (without oxygen). The fermented mixture (commonly known as the beer mash) is then distilled to recover the ethanol. Distillation is a process in which a liquid mixture is heated to vaporize the components having the highest vapor pressures (lowest boiling points). The vapors are then condensed to produce a liquid that is enriched in the more volatile compounds.

With the ever-increasing depletion of economically recoverable petroleum reserves, the production of ethanol from vegetative sources as a partial or complete replacement for conventional fossil-based liquid fuels becomes more attractive. In some areas, the economic and technical feasibility of using a 90% unleaded gasoline-10% anhydrous ethanol blend (“gasohol”) has shown encouraging results. According to a recent study, gasohol powered automobiles have averaged a 5% reduction in fuel compared to unleaded gasoline powered vehicles and have emitted one-third less carbon monoxide than the latter. In addition to offering promise as a practical and efficient fuel, biomass-derived ethanol in large quantities and at a competitive price has the potential in some areas for replacing certain petroleum-based chemical feedstocks. Thus, for example, ethanol can be catalytically dehydrated to ethylene, one of the most important of all chemical raw materials both in terms of quantity and versatility.

SUMMARY

The present invention is a method for preheating beer including providing a first heat exchanger, comprising a first outlet stream at a first temperature; providing a second heat exchanger, comprising a hot heat transfer stream, a first flow control valve situated within said hot heat transfer stream, a second outlet stream at a second temperature, a temperature sensor situated within said second outlet stream; wherein said first outlet fluid comprises a first inlet stream, and a second flow control valve situated within said first inlet stream; determining said second temperature with said temperature sensor; comparing said second temperature to a predetermined temperature range; performing an operation selected from the group consisting of: maintaining said first flow control valve in a closed position, and maintaining said second flow control valve in an open position, if said second temperature is within said predetermined temperature range, modulating said first flow control valve in order to effect heat transfer between said hot heat transfer fluid and said first inlet fluid, such that said second temperature within said predetermined temperature range, and maintaining said second flow control valve in an open position, determining if said second temperature is not within said predetermined temperature range if said first control valve is in the fully open position, and then closing said second flow control valve, closing said first flow control valve, and redirecting said first outlet stream away from said second heat exchanger.

DESCRIPTION OF PREFERRED EMBODIMENTS

Fouling is the buildup of material on the heat transfer surface that reduces the ability of heat to be transferred across the surface. Fouling is an inevitable part of the application of heat transfer surfaces to the beer stream to heat the beer. Typically, there are two beer preheaters in order to address the issue of fouling.

The beer typically found in a dry mill ethanol plant contains all the products of fermentation as well as the components of the grain (corn, sorghum, barley, wheat, etc) that pass through the fermentation process.

While the main desired product of fermentation is ethanol, one of the other products that may either be passed through, or developed as a fermentation product, is oxalic acid. Oxalic acid forms calcium oxalate in the presence of calcium ions. It is the combination of proteins and chiefly an organic salt, calcium oxalate, that can deposit and buildup on the heat transfer surface, reducing its effectiveness. When a typical ethanol plant starts up, it has been found that the beer preheaters foul rather quickly. The temperature out of the exchanger typically deteriorates as an indication of this fouling. (trending lower and lower beginning within 30 minutes and deteriorated sometimes as soon as 2 to 3 hours.)

In order to address this problem, in one embodiment of the present invention, in order to reliably produce a consistent feed temperature and have a reasonable frequency between cleanings, a hot utility stream is introduced, such that it will continue to drive the temperature higher despite the increased fouling that predictably occurs. In one embodiment of the inventive technique, a hot utility is utilized (in one embodiment, steam is used) along with the capability of a plate and frame exchanger to accept more than one heating media utilizing different in and out ports. The result is the decoupling of the incoming beer temperature and the fouling from determining the outlet beer temperature from the heat exchanger.

In one embodiment of the present invention, when the outlet beer temperature remains sufficiently high, the steam heat control valve remains in the closed position. As the beer temperature begins to drop, the steam supply valve is gradually opened to drive the temperature to the needed value. As fouling is still occurring it is eventually necessary to clean the heat exchanger so the process is switched to the standby exchanger and the fouled heat exchanger is cleaned.

In another embodiment, a separate heat exchanger may be utilized (in one embodiment, a shell and tube type) with steam to provide a consistent beer temperature output. There may be an issue of fouling on a single exchanger that may make it difficult to clean hence in one embodiment upgrading both exchangers may be done.

Other types of exchangers will also work, spiral exchangers, block exchangers, multiple styles of shell and tube exchangers, as well as direct injection of steam. Under certain conditions, incorporating the additional heating in the plate and frame exchanger is the least expensive approach. Other quantities of exchangers will work. In one embodiment, it is possible to have three of each type of exchanger or even more, although the capital expense would be higher. In another embodiment of the present invention, warming media other than steam, may be used, such as hot oil (Therminol for example), would work but would also be additional expense.

In one embodiment, the steam may be added to the previous heat exchangers (2) or upsteam of one or both of the existing exchangers, but would then have had the control lag between the output temperature needed and the response by the steam control valve. The cost to change the previous exchanger would have been much more expensive including radical piping changes.

If the pressure of the steam is too high it will accelerate fouling on the beer side of the exchanger reducing the time between cleaning. Flow rates are not limited accept to the size of plant being built, multiple exchangers can be run in parallel to accomplish this task. 

1. A method for preheating beer comprising: providing a first heat exchanger, comprising a first outlet stream at a first temperature, providing a second heat exchanger, comprising a hot heat transfer stream, a first flow control valve situated within said hot heat transfer stream, a second outlet stream at a second temperature, a temperature sensor situated within said second outlet stream, wherein said first outlet fluid comprises a first inlet stream, and a second flow control valve situated within said first inlet stream determining said second temperature with said temperature sensor, comparing said second temperature to a predetermined temperature range, performing an operation selected from the group consisting of: maintaining said first flow control valve in a closed position, and maintaining said second flow control valve in an open position, if said second temperature is within said predetermined temperature range, modulating said first flow control valve in order to effect heat transfer between said hot heat transfer fluid and said first inlet fluid, such that said second temperature within said predetermined temperature range, and maintaining said second flow control valve in an open position, determining if said second temperature is not within said predetermined temperature range if said first control valve is in the fully open position, and then closing said second flow control valve, closing said first flow control valve, and redirecting said first outlet stream away from said second heat exchanger.
 2. The method for preheating beer of claim 1, wherein said second temperature is not within said predetermined temperature range if said first control valve is in the fully open position because said second heat exchanger is fouled.
 3. The method of preheating beer of claim 2, wherein said fouling is due to proteins and calcium oxalate buildup.
 4. The method of preheating beer of claim 1, wherein said second heat exchanger is of the type selected from the group consisting of plate-in-frame, shell-and-tube, spiral, block, and direct contact.
 5. The method of preheating beer in claim 1, wherein said hot heat transfer stream comprises stream.
 6. The method of preheating beer in claim 1, wherein said hot heat transfer stream comprises therminol.
 7. The method of preheating beer in claim 1, wherein said predetermined temperature range is between 175° F. and 185° F.
 8. The method of preheating beer in claim 1, wherein said second heat exchanger further comprises two or more heat exchangers in parallel.
 9. The method of preheating beer in claim 1, wherein said redirection comprises: providing a third heat exchanger, comprising said hot heat transfer stream, a third flow control valve situated within said hot heat transfer stream, a third outlet stream at a third temperature, a second temperature sensor situated within said third outlet stream, wherein said first outlet fluid comprises a second inlet stream, and a fourth flow control valve situated within said second inlet stream determining said third temperature with said second temperature sensor, comparing said third temperature to the predetermined temperature range, performing an operation selected from the group consisting of: maintaining said third flow control valve in a closed position, and maintaining said third flow control valve in an open position, if said third temperature is within said predetermined temperature range, modulating said third flow control valve in order to effect heat transfer between said hot heat transfer fluid and said first inlet fluid, such that said third temperature within said predetermined temperature range, and maintaining said fourth flow control valve in an open position, determining if said third temperature is not within said predetermined temperature range if said third control valve is in the fully open position, and then closing said third flow control valve, closing said third flow control valve, and redirecting said first outlet stream away from said third heat exchanger. 